1. Field of the Invention
The invention relates to a process and apparatus for plasma treatment. More particularly, the invention relates to an improved process and apparatus for plasma treatment in which the plasma generation and the treatment are effected in separate chambers.
2. Description of the Prior Art
Processes for the production of semiconductor devices include many steps in which gas treatment is carried out. In gas treatment steps for, in particular, dry etching, chemical vapor deposition (CVD), and the like, uniformity of treatment is the most important factor. The uniformity of treatment in these gas treatment steps is highly affected by conditions of the treating gas flow formed in the treating region.
For the selective etching of semiconductor layers, insulator films, interconnection layers, and the like, there has been employed, for example, a plasma etching apparatus including a separate plasma generating chamber and a treating chamber, such as is schematically shown in FIG. 1 (see, e.g., Japanese Examined Patent Publication (Kokoku) No. 53-14472). In FIG. 1, 1 denotes a microwave generator, 2 a plasma generating chamber, 3 an etching gas feeding pipe, 4 a gas passageway, 5 a gas inlet, 6 a treating chamber, 7 an evacuation opening, 8 a material to be treated, 9 arrows indicating the direction of the gas flow, and P plasma.
In an apparatus having such a construction, at etching gas is converted into activated particles in the plasma generating chamber 2, and the activated particles are blown into the treating chamber 6 directly from the gas inlet 5. The activated particles are reacted with the material 8 in the chamber 6, and are then discharged. The etch rate of the material 8 to be treated depends on the accession percentage of the activated particles to the surface of the material to be treated and on the proportion of the elimination of the reaction product. Thus, the etch rate is highly affected by the positions of the gas inlet 5, evacuation openings 7, and the like. Thus, when a polycrystalline silicon layer of a thickness of about 4,000 .ANG., formed on a substrate of a diameter of 5 in., is etched on an apparatus of the above-mentioned construction, using a carbon tetrafluoride (CF.sub.4)/oxygen (O.sub.2) mixture having a usual composition as the etching gas, at a gas pressure of about 0.3 torr., a 10% to 20% variation of the etch rate occurs in the surface area, and the width of the formed pattern varies by 0.15 .mu.m or more.
The above-mentioned variation in etch rate may be improved by further reducing the gas pressure in the treating chamber. However, in this case, the reduction of the gas pressure for the purpose of lowering the etch rate extensively may result in the problem of a notable reduction in the amount of the activated particles.
There has also been employed an apparatus of a construction, as shown in FIG. 2, wherein a plasma generating chamber 2 and a treating chamber 6 are separated by a plasma regulating panel 11 having punched holes (see, e.g., Japanese Unexamined Patent Publication (Kokai) No. 57-48226). In this apparatus, an etching gas introduced from an etching gas feeding pipe 3 into the plasma generating chamber 2, is converted into activated particles by irradiating the etching gas with microwaves from a microwave generator 1 through a waveguide 12 and a microwave transmitting window 13, thereby generating plasma P. The activated particles are then introduced into the treating chamber 6 which has been evacuated through evacuation openings 7 by the pressure difference, from a plurality of gas introducing holes 14 formed in the plasma regulating panel 11, and act to etch a material 8 to be treated.
In an apparatus having such a construction, however, the variation of etch rate cannot be reduced even if the gas introducing holes are changed in number, size, or shape. The arrangement of the holes in the panel 11 and the direction of the gas flow being discharged may also cause variation in the etch rate, particularly when a few holes having a small diameter are provided. For example, when a polycrystalline silicon layer of a thickness of about 4,000 .ANG., formed on a substrate of a diameter of 5 in., is etched using a mixed carbon tetrafluoride (CF.sub.4)/oxygen/O.sub.2 gas as the etching gas at a gas pressure of 1.0 to 2.0 torr., the width of the formed pattern inevitably varies more than 0.3 .mu.m. Furthermore, it is difficult to alter the construction of the plasma regulating panel so as to obtain the best uniformity of the etching, even when the etching conditions such as the composition of the etching gas and the gas discharging rate are varied.